In this paper, selecting geological surveying area in Yantai city in Shandong Peninsula Blue Economic Zone as the research area, which covers about 636km2, 10 factors have been from 136 water quality monitoring results have been evaluated. Comprehensive index method is selected as the evaluation method, and the application of entropy weight in groundwater quality evaluation has been introduced in detail. The water quality in the study area can be divided into five areas, Ⅰ~ Ⅲ type water account for a total area of 40.1%, while Ⅳ and Ⅴ water account for a total area of 59.9%. The overall water quality is general. The main reasons are large amounts of industrial sewage and domestic sewage discharge, large amounts of chemical fertilizer and pesticide use, and large amounts of underground water extraction. The poor areas are mainly distributed in Dajijia town in the development zone, Guxian town, Sunjiatan in Fushan district, Douyuzhen town in Fushan district, north of Sunjiatan in Laoshan district, south of Bajiao townYongfuyuan, north of Laishan streetJiejiazhuang street, Yangmadao island, Wuning town in Muping city, and downstream of the river and coastal areas. Superscalar factors include nitrites, nitrates, chloride, total dissolved solids (TDS), total hardness, ammonia nitrogen, cadmium, lead, volatile phenol, etc. Through analysis and comparison, the evaluation result of entropy weight comprehensive index method is reliable and worth popularizing. It is showed that the calculation process of this method is simple and reasonable, and the result is objective, reliable and reasonable.